Direct reduction of iron oxide and other metallic oxides may be conducted in rotary hearth furnaces (RHF) using pelletized or briquetted compacts containing a carbonaceous reductant and deposited upon a rotating hearth. Briefly, a RHF is a continuous reheating furnace generally having an annular inner wall circumscribed by a spaced annular outer wall. The space there between includes a circular rotating hearth. Burners may be installed in the inner and outer walls and in the roof. Gases from the furnace are permitted to vent through a flue located in the roof.
Compacts are usually loaded (dropped) onto the rotating hearth by a conveyor or chute. After the material is conveyed along the hearth path it is removed by a discharge auger. The discharge auger typically consists of a central shaft with solid helical metal flights attached thereto and projecting away from the central shaft. High temperatures and the presence of oxygen or one or more of sodium, sulfides, chlorides, fluorides, potassium, lead, zinc, tin, iron, nickel and chromium within the RHF oftentimes corrodes and erodes the auger and renders the auger ineffective. To lessen the effects of the high temperatures (1300-2300 degrees Fahrenheit)(704-1260 degrees Celsius), a cooling fluid is frequently passed through the auger. See U.S. Pat. Nos. 3,443,931 and 4,636,127, incorporated herein by reference. It is intended that with sufficient flow rate, the fluid cooling maintains the central shaft of the auger within acceptable metal material operating temperatures. However, it will be appreciated that cooling of the core of the auger has some effect on modulation of the flight tip temperature, the flight tip temperature is determined primarily by the environment temperature. Although some heat is conducted through the helical flight to the fluid cooled central shaft, the high radiation heat transfer from the furnace and the limited thermal conductivity of the helical flight often causes the tips of the helical flight to operate over the maximum desired operating temperature of the metal alloys forming the helical flight thereby leading to premature auger failure.
It will be appreciated that failure of the auger necessitates replacement of the auger and unwanted downtime, high maintenance and labor costs, and inefficient use of the furnace which, in turn, leads to higher unit costs. In view of the foregoing, it will be appreciated that there is a significant need for an improved furnace discharge assembly.
An object of the present invention is to provide an improved furnace discharge assembly. Another object of the present invention is to provide a furnace discharge assembly including a discharge auger capable of better withstanding the high operating temperatures of the furnace. Yet another object of the present invention is to provide a furnace discharge assembly including a discharge auger and an external coolant spray to maintain the metal alloy helical flights at an acceptable operating temperature for oxidation and wear resistance. Still another object of the present invention is to provide a furnace discharge assembly that is simple and economical to manufacture and/or operate.